This invention relates to data transmission systems, and in particular to apparatus for shunting data terminals.
A well-known technique for supplying data from a central processor to a plurality of data terminals includes the series connection of said terminals, in a serial data loop, to output and input terminals of said central processor. The data received by the first data terminal in said series connection is sent on by said first terminal to the second series connected terminal and so on around the serial loop and back to the central data processor. With such a system, whenever one of the data terminals becomes inoperative, it interrupts operation of the entire data loop. Such interruptions often cause unacceptable system downtime. Several approaches have been employed for putting the remaining non-defective terminals back into an operative data loop.
One well-known technique is to employ a manual bypass switch for each data terminal which has the capability of completely disconnecting the data terminal from the data loop while at the same time providing a direct shunt which reestablishes the series circuit and thus allows data to pass to the remaining terminals. With such arrangements the bypass switches for the various terminals are oftentimes mounted on a common switchboard to provide a central location for connecting or disconnecting each of the terminals in the loop.
U.S. Pat. No. 4,035,770 issued to Sarle on 12 July 1977, discloses a scanning system for locating and isolating a faulty terminal in a series connection of terminals. With that system, when the data loop is broken due to a faulty terminal, a scanner circuit sequentially energizes bypass relays associated with each of the terminals. When the offending terminal is reached in the sequence, the data loop is reinstated and said offending terminal is located and eliminated from the loop at the same time. This arrangement requires that the data loop be out of commission during the time that the scanning is going on. For a large system this scanning time, which represents downtime, may be undesirably long.
U.S. Pat. No. 4,015,241 issued to Takezoe on 29 Mar. 1977 shows in FIG. 2 thereof a pair of bypass switches Ra and Rb which are used to shunt a communications terminal. Nothing in this patent appears to disclose what causes the switches to be actuated. The patent does disclose an arrangement for checking the working condition of an addressed terminal and for transmitting information to said address terminal only when said terminal is in a working condition. The purpose of Takezoe is to increase the transmission efficiency of the system by eliminating the time that would be wasted during addressing of non-working terminals.
U.S. Pat. No. 3,876,983 issued Apr. 8 1975 and its reissue Pat. No. Re. 28,958 issued Sept. 7 1976 to Zafiropulo, et al. show a system for bypassing portions of a series loop with portions of a parallel loop. It is an example of a very complex arrangement for locating and isolating faulty data terminals.
U.S. Pat. No. 3,716,834 issued to Adams on Feb. 13 1973 discloses a data transmission system for locating and isolating circuit faults. Interrogation pulse signals are sent out from a central station to remote terminals, and reply signals are analyzed to determine the nature and location of the fault. This again is a complex arrangement requiring specialized central station interrogating and receiving apparatus.
U.S. Pat. No. 3,601,806 issued to Heimbigner on Aug. 24 1971 shows a complex bidirectional transmission system which includes the capability of deactivating and bypassing certain remote terminals using a sequential interrogation arrangement accomplished by means of clock pulses transmitted from a master station to the remote terminals.
U.S. Pat. No. 3,519,750 issued to Deresin, et al., on July 7 1970 discloses a complex communications system employing a second standby channel in combination with complex electronic switching gear for automatically reestablishing a broken transmission link between succesive stations.
None of the above-mentioned patents disclose or suggest the simple, instantaneously and automatically operating terminal shunting circuit of the instant invention.
It is therefore an object of this invention to provide automatic means for bypassing an inoperative data terminal in a series connection of data terminals, wherein said inoperative data terminal is instantaneously disconnected and shunted.
It is a further object of this invention to provide easily interpreted visual indications of the operating condition of a data terminal.
It is yet a further object of this invention to provide an audio and visual alarm system for designating an inoperative data terminal, including a manually operated switch capable of activating said automatic shunt while simultaneously disconnecting said remote alarm system.